Hi Jose, I finished this project a couple of weeks ago.
I wanted to thank you for getting back to me with such helpful information, and I also wanted to follow up with my solution to the SPI problem (for future users). I ended up using a different driver file for SPI0 than the one provided by Adafruit: http://elinux.org/BeagleBone_Black_Enable_SPIDEV Guide for adding SPI driver: http://stackoverflow.com/questions/21276090/beaglebone-black-enable-spi-interface For me, the easiest method for verification was to read the DEVID register on the accelerometer. #python code: print spi.xfer2([0x80,0x00]) This prints a list of 2 bytes. With how I understand SPI to work, the second byte in the printed list should always be the DEVID. The first byte may or may not be the DEVID. This is just one of the nuances of the data flow of SPI. -Stuart On Sunday, March 30, 2014 3:43:07 PM UTC-4, José Luis Redrejo wrote: > > Hello Stuart, I've been using BBB to communicate with another Analog > Devices device (ADE7753) , and I can confirm you that it works. > Have you tried to do a loopback test before connecting the ADXL275? > Just use a wire in the BBB to join DI and DO in P9, and run this > program: > > > from Adafruit_BBIO.SPI import SPI > > spi = SPI(0,0) > spi.mode=2 > > spi.msh=2000000 > spi.open(0,0) > > print spi.xfer2([32, 11, 110, 22, 220]) > spi.close() > > You should see 32,11,110,22,220 in your terminal as it's returned by > the spi instruction. > > You don't need > spi.cshigh = low > because that's its default value. > > If the loopback test works, then you can try with the device. I can > confirm you that using ADE7753 and adafruit python library I have need > some time to get it working, until I found out the trick. > > Regards. > José L. > > > > 2014-03-30 18:10 GMT+02:00 Stuart Reynard <[email protected]<javascript:>>: > > > I am working on a design project involving a BeagleBone Black and an > ADXL375 > > Accelerometer. > > > > Per the data sheet (attached), in order to enable the maximum sampling > rate > > of the ADXL375, I need my BBB to communicate with the ADXL375 over SPI > (I2C > > is not fast enough for this). > > > > I have used the Adafruit library for I2C just to test the functionality > of > > the ADXL375, and I can confirm that the accel. does in fact work. > However, I > > am unsure of how to even perform a simple read of the ADXL375 DEVID > register > > using SPI. I have included my steps for how I think a read should be > > performed, but I suspect that this process is incorrect as I get no > output. > > > > I am using the Adafruit BBIO library which I understand is just a python > > wrapper for the file spimodule.c. All of this is available here: > > > > https://github.com/adafruit/adafruit-beaglebone-io-python/ > > > > Based on that code, I am not sure if I will need to hold CS low using > one of > > the methods/variables of an SPI object or if the > writebytes()/readbytes() > > methods take care of this for me. In other words, I don't know if I > should > > be doing something like > > > > spi.cshigh = low > > spi.writebytes([list]) > > spi.readbytes(numBytes) > > > > OR if I can just do > > > > spi.writebytes([list]) > > spi.readbytes(numBytes) > > > > Process for reading from SPI (from python terminal): > > > > from Adafruit_BBIO.SPI import SPI > > > > #using SPI bus 0 on P9 of BBB, assuming i'm using dev0, not really sure > how > > to determine this, but I have no other peripherals connected > > spi = SPI(0,0) > > > > #set desired frequency, 2MHz > > spi.msh = 2000000 > > > > #per the ADXL375 datasheet, when performing a read, need to send a byte > > where bits 0-5 are address bits (DEVID register is 0x0), bit 6 is a > multiple > > bytes bit (for reading/writing multiple bytes), and bit 7 is a > read/write > > bit where read is '1' and write is '0' > > > > #so I use 0b10000000 or 0x80 and call writebytes > > spi.writebytes([0x80]) > > > > From here I receive no output, even if I do spi.readbytes(1), I get [0] > > back. > > > > I have a pretty good understanding of Linux, Python, C, and the concept > of > > SPI seems simple enough, but this is my first experience with a BBB. I > feel > > like I am missing something simple like setting CS low, which I don't > think > > is very clearly documented in the attributes for the SPI library. > > > > Here is some info about my BBB: > > lsb_release -a > > Distributor ID: Angstrom > > Description: Angstrom GNU/Linux v2012.12 (Core edition) > > Release: v2012.12 > > Codename: Core edition > > > > uname -a > > Linux beaglebone 3.8.13 #1 SMP Wed Sep 4 09:09:32 CEST 2013 armv7l > GNU/Linux > > > > I have also attached the breakout board user guide for the ADXL375. I > would > > be happy to come back with any additional info. > > > > Thanks, > > Stuart > > > > -- > > For more options, visit http://beagleboard.org/discuss > > --- > > You received this message because you are subscribed to the Google > Groups > > "BeagleBoard" group. > > To unsubscribe from this group and stop receiving emails from it, send > an > > email to [email protected] <javascript:>. > > For more options, visit https://groups.google.com/d/optout. > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
